Taking into account the lack of the fast travel option would you like supply lines to make workshops share their full inventory rather than just building materials?This would allow you to drop weapons,armour and stuff say in Tenpines bluffs and be able to retrieve said items at the castle for example,at the condition that the two belong to the same supply network?
An alternative would be to allow you to fast travel between settlements that belong to the same network.(After all,if it is safe for the provisioner it can't be that hard to go from A to B .